Sunday, May 08, 2016

Can humans listen like songbirds do?

Humans and songbirds share many interesting similarities with regard to their auditory processing capabilities. For example, we know that humans and European Starlings have similar frequency sensitivity, perceive the pitch of the missing fundamental, and parse multiple pure-tone sequences into separate auditory streams. At higher levels, the “musical” nature of birdsong has long been appreciated by humans, and some songbirds can readily learn to discriminate and imitate human melodic sequences (cf. Hoeschele et al., 2015).

Given these similarities, it is surprising to find a major difference in how humans and songbirds perceive sequences of tones. Humans readily recognize tone sequences that are shifted up or down in log frequency because the pattern of relative pitches is maintained (referred to as relative pitch). In contrast, songbirds appear to have a strong bias to rely on absolute pitch for the recognition of tone sequences (a pitch-shifted melody might well be perceived as an altogether different melody; Hoeschele et al., 2015).

Interestingly, a recent study by Bregman et al. (2016), contrasting pitch and spectral patterns, shows that birds perceive their song more like humans perceive speech (Shannon, 2016). More precisely, songbirds might attend more to the acoustic spectral shape than to the absolute pitch of the acoustic signal. Stimuli that preserve acoustic spectral shape, even in the absence of pitch, seem to allow for generalization of learned acoustic patterns. Hence it could well be that a sensitivity to spectral shape is what is shared between human and avian cognition of musical signals, while relative pitch is the preferred mode of listening for humans. And one could wonder: why is sound "super normally stimulated" in humans (see earlier entry), and can humans be made to change their listening mode in the direction of birds (or vice versa) when manipulating melody and spectral shape?